Abstract
Q. Zhao and L. Tong
"Distributed Opportunistic Information Retrieval in Sensor Networks: CSI-Based Carrier Sensing"
Submitted to IEEE Journal on Selected Areas in Communications: Special Issue on Self-Organizing Distributed Collaborative Sensor
Networks
, Nov., 2003.
We consider distributed information retrieval
for sensors networks with cluster heads or mobile access points.
The performance metric used in the design is
energy efficiency defined as the ratio of
the average number of bits reliably retrieved by the
access point and the total amount of energy consumed.
A distributed opportunistic transmission protocol is proposed
using a combination of carrier sensing and backoff strategy that
incorporates channel state information (CSI) of individual sensors.
By selecting a set of sensors with the best channel states to
transmit, the proposed protocol achieves the
upper bound on energy efficiency when the signal propagation
delay is negligible. For
networks with substantial propagation delays,
a backoff function optimized for energy efficiency
is proposed. The design of
this backoff function utilizes properties of extreme statistics
and is shown to have mild performance loss in
practical scenarios. We also demonstrate that
opportunistic strategies that use channel state
information may not be optimal when channel acquisition
at individual sensors consumes substantial energy. We show
further that there is an optimal sensor density for which
the opportunistic information retrieval is the most energy
efficient. This observation leads to the design of optimal sensor
duty-cycle.